Gas turbine engines (GTEs) produce power by extracting energy from a flow of hot gas produced by combustion of fuel in a stream of compressed air. In general, GTEs have an upstream air compressor coupled to a downstream turbine with a combustion chamber (combustor) in between. Energy is produced when a mixture of compressed air and fuel is burned in the combustor, and the resulting hot gases are used to spin blades of a turbine. In typical GTEs, multiple fuel injectors direct the fuel to the combustor for combustion. Combustion of typical fuels results in the production of some undesirable constituents, such as NOx, in GTE exhaust emissions. Air pollution concerns have led to government regulations that regulate the emission of NOx in GTE exhaust. One method used to reduce NOx emissions of GTEs is to use a well mixed lean fuel-air mixture (fuel-air mixture having a lower fuel to air ratio than the stoichiometric ratio) for combustion in the combustor. However, in some cases, using a lean fuel-air mixture may make combustion in the combustor unstable. To provide a stable flame while meeting NOx emission regulations, some fuel injectors direct separate streams of a lean fuel-air mixture and a richer fuel-air mixture to the combustor. The lean fuel-air mixture may provide low NOx emissions, while the richer fuel-air mixture may provide flame stabilization during periods of flame instability.
In some cases, the fuel injector may also be configured to direct both a liquid and a gaseous fuel to the combustor. Such a fuel injector, called a dual fuel injector, may enable the GTE to operate using both liquid fuel (such as, for example, diesel) and gaseous fuel (such as, for example, natural gas), depending upon the conditions and economics of any particular GTE operating site. In dual fuel injectors, one of a liquid or a gaseous fuel may be directed to the fuel injector to be mixed with air, and delivered to the combustor. Such a dual fuel injector may include both liquid fuel supply lines and gaseous fuel supply lines, along with suitable valves, to enable the liquid fuel supply to the injector to be switched off while the GTE is operating on gaseous fuel, and the gaseous fuel supply to the injector to be switched off while the GTE is operating on liquid fuel. However, even when the liquid or gaseous fuel is switched off, the corresponding fuel lines may still fluidly couple the multiple injectors of the GTE to each other. Minor variations in the air-fuel mixture (fuel to air ratio, amount of flow, etc.) delivered to the combustor through different fuel injectors may cause variations in the flame at the outlet (inlet into the combustor) of the different fuel injectors. These variations in the flame may cause pressure variations between the outlets of different fuel injectors (combustion induced circumferential pressure variation). The variation in pressure between the different injector outlets may cause ingestion of fuel and/or combustion gases into the inactive fuel lines. This inflow of fuel and/or hot combustion gases through the inactive fuel lines of one fuel injector and outflow through a second fuel injector is called cross-talk. Cross-talk may cause the fuel delivery system to become hot and cause damage.
U.S. Patent Publication number 2007/0044477A1 ('477 publication) to Held et al. discloses a gas turbine engine fuel nozzle that is configured to reduce cross-talk. The fuel nozzle of the '477 publication includes a first, a second, and a third passage extending coaxially along an axis of symmetry of the nozzle. The first, second, and third passageways include a nozzle at one end that extends into the combustor. Each of the passageways of the nozzle of the '477 publication also includes an inlet opening that is fluidly coupled to the combustor. The two innermost passageways of the '477 publication direct a fuel to the combustor. The outermost passageway of the '477 publication is configured to direct steam to the combustor, and includes an additional inlet opening upstream of the nozzle. The inlet openings of the third passageway are located in such a manner that a pressure differential across the inlet openings facilitates providing the driving pressure for a purge flow across the nozzle tip and protection against circumferential pressure gradients that may tend to induce cross-talk. While the approach of the '477 publication may reduce cross-talk in some applications, it may have disadvantages. For instance, it may not be applicable to a gas turbine engine application that does not include steam in the fuel supply system. Additionally, the approach of the '477 publication may not reduce cross-talk in a dual fuel injector where fuel lines associated with one type of fuel may be inactive when the turbine engine is operating using the other type of fuel.